The application's broad, long-term objectives are the development of highly enantio- and diastereoselective chiral reagents/methods for the efficient synthesis of a variety of 100% enantiomerically pure substances, which are in great demand in natural product synthesis, biomedical and pharmaceutical research. The specific aims of the proposal include: (1) Asymmetric cyclic hydroboration to achieve a highly stereoselective synthesis of optically pure trans-[n,n']-fused rings (n = 5,6,7,8...; n' = 5,6,7,8). (2) Development of newer and more powerful chiral auxiliaries for achieving 100% stereo-selective asymmetric hydroboration. (3) Development of practical methods for the synthesis of a variety of 100% enantiomerically pure organic compounds from readily available optically pure boron intermediates. (4) Development of convenient methods to recycle the chiral auxiliary after allyl- and crotylboration in order to make our reagents highly cost- effective, even for industrial applications. (5) Investigation of asymmetric crotylborations of various aldehydes at - 100 oC to achieve the highest possible enantio- and diastereoselectivities, which can directly benefit polyether antibiotic synthesis. (6) Exploration of the asymmetric allyl- and crotylborations of representative heterocyclic aldehydes to develop powerful new methods for the asymmetric synthesis of a multitude of heterocyclic natural products. (7) Exploration of new strategies/new reagents for the asymmetric synthesis of (a) 4-substituted-gamma-lactones, to provide valuable routes to optically active pheromones and other natural products; (b) substituted spiroketals, to offer enantioselective routes to macrolide antibiotics; (c) 6-substituted-5,6-dihydro-2-pyranones, to develop stereoselective routes to many biologically important natural products (see background and significance); (d) substituted tetrahydrofurans and tetrahydropyrans, to provide completely stereoselective routes to various monocarboxylic acid ionophores. (8) Application of powerful new allyl- and crotylborane reagents and favorable experimental conditions to solve the mismatch problems encountered in double asymmetric synthesis.